Fix parsing of pipeline operator in arrow bodies

This should resolve the scoping issues we're seeing in the transform.

packages/babel-parser/src/parser/expression.js

@@ -331,8 +331,11 @@ export default class ExpressionParser extends LValParser {
     const prec = this.state.type.binop;
     if (prec != null && (!noIn || !this.match(tt._in))) {
       if (prec > minPrec) {
-        const node = this.startNodeAt(leftStartPos, leftStartLoc);
         const operator = this.state.value;
+        if (operator === "|>" && this.state.inFSharpPipelineDirectBody) {
+          return left;
+        }
+        const node = this.startNodeAt(leftStartPos, leftStartLoc);
         node.left = left;
         node.operator = operator;
         if (
@@ -1185,9 +1188,11 @@ export default class ExpressionParser extends LValParser {
     const oldMaybeInArrowParameters = this.state.maybeInArrowParameters;
     const oldYieldPos = this.state.yieldPos;
     const oldAwaitPos = this.state.awaitPos;
+    const oldInFSharpPipelineDirectBody = this.state.inFSharpPipelineDirectBody;
     this.state.maybeInArrowParameters = true;
     this.state.yieldPos = 0;
     this.state.awaitPos = 0;
+    this.state.inFSharpPipelineDirectBody = false;
 
     const innerStartPos = this.state.start;
     const innerStartLoc = this.state.startLoc;
@@ -1241,6 +1246,7 @@ export default class ExpressionParser extends LValParser {
     this.expect(tt.parenR);
 
     this.state.maybeInArrowParameters = oldMaybeInArrowParameters;
+    this.state.inFSharpPipelineDirectBody = oldInFSharpPipelineDirectBody;
 
     let arrowNode = this.startNodeAt(startPos, startLoc);
     if (
@@ -2347,6 +2353,8 @@ export default class ExpressionParser extends LValParser {
 
     const node = this.startNode();
     this.state.potentialArrowAt = this.state.start;
+    const oldInFSharpPipelineDirectBody = this.state.inFSharpPipelineDirectBody;
+    this.state.inFSharpPipelineDirectBody = true;
 
     node.body = this.parseExprOp(
       this.parseMaybeUnary(),
@@ -2356,6 +2364,8 @@ export default class ExpressionParser extends LValParser {
       noIn,
     );
 
+    this.state.inFSharpPipelineDirectBody = oldInFSharpPipelineDirectBody;
+
     return this.finishNode(node, "PipelineBody");
   }
 }

packages/babel-parser/src/tokenizer/state.js

@@ -79,6 +79,7 @@ export default class State {
 
   // For the F# plugin
   soloAwait: boolean = false;
+  inFSharpPipelineDirectBody: boolean = false;
 
   // Check whether we are in a (nested) class or not.
   classLevel: number = 0;

packages/babel-parser/test/fixtures/experimental/pipeline-operator/proposal-fsharp-arrow-and-array-in-body/input.js

@@ -0,0 +1 @@
+x => x |> [y => y + 1] |> z => z * 2

packages/babel-parser/test/fixtures/experimental/pipeline-operator/proposal-fsharp-arrow-and-array-in-body/options.json

@@ -0,0 +1,3 @@
+{
+  "plugins": [["pipelineOperator", { "proposal": "fsharp" }]]
+}